The goal of this proposal is to obtain an understanding of the fate of viral DNA after the viral RNA has been converted to DNA by the concerted action of the viral DNA polymerase and ribonuclease activities. The two objectives of this proposal are to understand the process of integration of viral DNA into host DNA and to understand the process of formation of virus DNA circles. Our preliminary work demonstrates that both the integration and circularization reactions can be studied in vitro. Objective 1. Characterization of the integration reaction. Specific Aims include: A. Characterization of virus and cell specified proteins in the preintegration complexes that are present in the cytoplasm and the nucleus of the newly infected cell. B. Reconstruction of an efficient integration reaction using purified virus and cell proteins. Objective 2. Understanding the reactions which govern formation of viral DNA circles. Three types of viral DNA circles are made in infected cells, 1-LTR circles, simple 2-LTR circles, and 2-LTR circles thought to be the product of autointegration reactions. Recent progress permits the circularization reactions to be studied in vitro. Specific aims include: A. Determination of the optimal conditions for the circularization of viral DNA in vitro. B. Characterization and purification of host-specific proteins required for the formation of 1-LTR and 2-LTR circles. The process of HIV-1 integration is a critical part of the virus life-cycle. Our preliminary studies have opened this area for systematic investigation. Understanding this process may provide opportunities for the development of a novel class of antiviral drugs.